1. Field of the Invention
The present invention relates to a radiation emission control method, apparatus and the program. More specifically, the present invention relates to a radiation emission control method, apparatus and the program for obtaining a radiation image of a test subject when the subject is in an intended respiratory phase.
2. Description of the Related Art
Generally, chest and abdominal radiographs, including digital images, are imaged or obtained as photographs for use to perform diagnostic image interpretations. Chest radiographs are often imaged when a patient as the test subject is in a maximum inhaled state to obtain a widest possible chest region for imaging, or they are imaged serially in each respiratory phase in order to observe the chest region under respiration. On the other hand, abdominal radiographs are often imaged when the test subject is in a maximum exhaled state to obtain a widest possible abdominal region for imaging. As described above, chest and abdominal radiographs are imaged when the test subject is in an intended respiratory phase which is dependent on the intended use.
In the mean time, in imaging a test subject when the subject is in an intended respiratory phase, it is customary that the subject is directed by the radiographer to hold the breath at the intended respiratory phase, since the subject may control its own respiratory phase.
But, if the test subject is an individual having difficulties to communicate with the radiographer, such as an infant or the like, or when radiographs are to be imaged sequentially at each respiratory phase in order to obtain a dynamic image of the test subject under respiration, it may be difficult for the test subject to hold the breath at each of the respiratory phases.
Under these circumstances, various methods for detecting respiratory phases of a test subject through some way or another are proposed for radiographing the subject in synchronization with an intended respiratory phase.
One such method is proposed as described, for example, in Japanese Unexamined Patent Publication Nos. 2003-290184, 2003-290202, and 2003-298939. The method detects respiratory phases of a test subject through a dynamic x-ray image obtained by continuously x-raying the test subject, and radiographing the test subject in synchronization with an intended respiratory phase. Another type of method is also proposed as described, for example, in U.S. Patent Application Publication No. 20040030235 and Japanese Unexamined Patent Publication Nos. 2000-201922, 2001-299942, 2002-360543 and 2004-057559. The method detects respiratory phases of a test subject by measuring the displacement of the body surface of the test subject using a distance measuring means having an LED or LD (laser diode), and radiographing the subject in synchronization with an intended respiratory phase.
The method that uses a dynamic x-ray image to detect respiratory phases of a test subject, however, has the disadvantage that the subject is exposed to an excessive amount of radiation dosage. While, in the method that detects respiratory phases of a test subject by measuring the displacement of the body surface of the subject using a distance measuring means, the position of the body surface of the subject is directly measured. Thus, it tends to have detection errors arising from the changes in the posture of the test subject, and suffers from the problem that it may not provide stable accuracy for detecting respiratory phases of the subject.